It is known that rehabilitation and physical therapy is a major contributor of treatment in order to restore the physical mobility and functionality of patients with injuries affecting ambulation. It is also known that during the course of such treatments an objective evaluation coupled with the medical practitioner's subjective evaluation can change the results and course of treatment dramatically. Such objective evaluation may be obtained by employing a gait analysis system. Typically, the movements of a patient undergoing a physical therapy regiment is periodically measured by a gait analyzer. However, previous studies have revealed that the test/retest repeatability of prior art gait analyzers are unreliable. As physicians and care providers increasingly demand justification for the quality and type of treatment given to patient, the effectiveness and reliability of equipment is of ever-increasing importance.
Some of the prior art gait analyzers employ pressure sensors to measure a change in pressure by converting a change in resistance using a plurality of transducers arranged in a row/column array fashion and where each transducer can be uniquely addressed by the electronic control signals.
U.S. Pat. No. 5,033,29 to Podoloff et al. discloses a flexible tactile sensor for measuring foot pressure distributions. Podoloff teaches a force and pressure sensor provided with two sets of parallel electrodes positioned facing one another and arranged so that electrodes of one set cross the electrodes of the second set to create a plurality of electrode intersections. Between the electrodes at each intersection lie an adhesive layer for securing the first and second electrodes in facing relationship. The adhesive layer is of an adjustable thickness which serves to permit preloading or to provide a variable threshold level for the sensor. Use of this sensor may, however, provide discomfort to the user since it must be inserted within the user's shoe or some other orthotic device in order to measure the force between the wearer's foot and the supporting surface beneath the foot.
The force and/or pressure transducer arrays disclosed in U.S. Pat. No 5,253,656, U.S. Pat. No. 5,033,291 and U.S. Pat. No. 4,734,034 are designed to identify forces exerted between a body part and an external surface and are not suitable for the objects of this invention. The transducer arrays as disclosed in these prior art references utilizes adhesive as a separator between top and bottom layers upon which the arrays are disposed. When a load is applied to a sensor, a minimum load is required in order to compress the adhesive so as to bring the top and bottom layers into contact. This minimum load depends on the thickness and resilience of the adhesive and the thickness of the flexible backing material from which the top and bottom layers are fabricated. Further increases on the load changes the resistance between the top and bottom layers in some linear or exponential fashion. Upon removal of the load, the adhesive separator is responsible for breaking the contact between the top and bottom layers. The time required to accomplish this depends on the characteristics of the adhesive and the thickness of the flexible backing materials of the top and bottom layers. These variables affect the linearity of the sensor. Additionally, changes in the thickness and resilience of the adhesive separator result over the passage of time, as a result of environmental conditions, the frequency of use and the size of the load applied. These conditions render the transducer arrays disclosed in these references as single-use sensors.
The amount of time required to overcome the adhesive response and break the contact between the top and bottom layers is the "turn-off delay". In the prior art devices disclosed in U.S. Pat. No. 5,253,656, U.S. Pat. No. 5,033,291 and U.S. Pat. No. 4,734,034, the turn-off delay is very high and produces extensive hysteresis which, in turn, effects the turn-off linearity of the sensor on the array. In order to minimize hysteresis, the separation time of the adhesive separator must be increased. These prior art references accomplish this by utilizing very thin top and bottom flexible layers of backing material. The use of thin layers of backing material produces multiple adverse side effects, such as deformation of sensing area when rolled, and reduction of the minimum load required to first compress the adhesive separator and commence sensor activity. Reduction of the minimum load is undesirable because it makes it easier for a load to trigger neighboring sensors.
These prior art references also assume that the load surface are in contact with the sensor is equal or greater than the active area of the sensor. When the load surface area becomes smaller than the sensor active area, the results are rendered invalid because the determination of whether the actual load changed or the load surface area changed cannot be made.
Other instruments have been explored for dynamic gait analysis. U.S. Pat. No. 4600, 016 to Boyd et al. describes elongated platform upon which the subject may stride and a moveable camera disposed below the platform for viewing the plantar aspects of the subject's foot. The camera which is mounted on a trolley driven by a cable and pulley is connected to a belt worn by the subject so that the camera is moved synchronously with the subject ambulating on the platform. A fluorescent light is placed on one edge of the platform; the remaining edges being covered with reflective material to minimize loss of light. The surface of the platform is heated to minimize loss of light. The surface is heated to minimize condensation. However, this instrument is not portable and it does not measure the relative forces of the plantar aspects of the foot. It is obvious that by attaching a cable to move the camera below will alter the natural gait of the subject. Also, lights under the surface of a transparent platform will increase the field of depth and this alters the natural gait.
U.S. Pat. No. 4,136,682 to Pedotti and U.S. Pat. No. 4,195,643 to Pratt disclose apparatuses and methods for evaluating locomotive functionality which comprise rigid platforms with force and/or pressure transducing members. Such methods including methods utilizing cinematography instruments are not suitable to accurately identify the geometry and geometrical outline of the footfalls and are not suitable for portability especially for use in evaluating home care patients.
The present invention employs an apparatus and a method of manufacturing said apparatus which is directed to measuring the pressure, spatial and temporal parameters of events taking place during the gait of a patient so that the outcome of treatment may be assessed. Such measurements enable health care providers to document the provided benefits and the degree of benefit provided. The present invention not only addresses the problems associated with the accuracy and linearity of the transducer, but also with the problems associated with the minimum scan time of the array, which is the time required to sample each and every transducer of the array at least once. The present invention also addresses the problems associated with the turn-on hysteresis when a load is applied, the turn-off hysteresis when a load is removed, the miss-triggering of the pressure transducers located in close vicinity to the load, and the location and method of interconnection to the electronic controls such as to produce a portable long walkway that can be rolled onto a drum for storage and relocation.